Direct heated cathode member for an electron tube



Nov. 17., 1970 YUKIO TAKANASHI ERTAL 3,541,382

DIRECT HEATED CATHODE MEMBER FOR AN ELECTRON TUBE Filed Dec. 9, 1968 3 Sheets-Shed 1 T 3 l a 10} 815 g 5 Y- 1) j 4X ILIJHII g 4 IHUI &

1970 Y'UKlO TAKANASHI A 3,541,382

DIRECT HEATED CATHODEMEMBER FOR AN ELECTRON TUBE Filed Dec. 9, 1 968 I i s Sheets-Sheet? T1 EMITTING MATERIAL ISHEATER- fi I .I I, l I4 ZELASTIC jv l4 I. 17 1? II 5 II 18 i 1 United States Patent U.S. Cl. 313-341 4 Claims ABSTRACT OF THE DISCLOSURE A direct heated cathode member for electron tubes is generally constructed in symmetric relationship. A ribbon-shaped heater is stretched over an insulating substrate with its major surface very close to and parallel to that of the substrate.

The present invention relates to a direct heated cathode for an electron tube, and more particularly to a direct heated cathode member suitably adapted for use in cathode ray tubes, etc.

With a certain type of electron tube, for example, a cathode ray tube incorporated in a television receiving set, it is preferred that the cathode be a direct heated type immediately operable upon the switching on of a power source. With such a direct heated cathode, it is required that the heater coated with a thermion emitting material be firmly stretched with a prescribed tension and that when the cathode is put into operation, the source of emitting thermions be maintained at a specified position relative to other electrodes. With a compact portable television receiving set, the electron source must to be free from displacement due to shakings which may occur while the receiving set is carried, and should also have a quake-proof structure.

The prior art cathode member of the cathode ray tube comprised heater supports disposed on a substrate made of an insulating material, such as ceramics, a ribbonshaped heater stretched across the heater supports, and a spring attached to a spring means affixed to the substrate to keep the ribbon-shaped heater under great tension by means of the spring. However, it was diflicult to keep the surface of the ribbon-shaped heater parallel to that of the ceramic substrate, and consequently it was difiicult to hold the thermion emitting source at a prescribed position. There were further drawbacks, for example, that the complicated arrangement failed to render the cathode member fully quake-proof, with the resultant necessity of machining the respective parts with extremely high precision and the intricate assembling steps also made the cathode member unsuitable for mass production.

It is accordingly an object of the present invention to provide a direct heated cathode member wherein a thermion emitting source always assumes a constant position even when the cathode is operated.

Another object of the invention is to provide a direct heated cathode member greatly resistant to mechanical shocks, such as shakings.

Still another object of the invention is to provide a direct heated cathode member which is suitably adapted for mass production, which is of simple construction, and whose parts can be machined and assembled with great ease.

Patented Nov. 17, 1970 ice According to the present invention, there is provided a direct heated electron tube cathode member comprising an insulating substrate having a pair of void spaces provided in opposite relationship, a pair of heater rests positioned adjacent to said void spaces in symmetrical relationship, a pair of metal strips fixed in opposite relationship on the substrate perpendicularly to its lengthwise direction in the void spaces so as to face the paired heater rests respectively, a pair of elastic metal strips each having one of its ends attached to the paired metal strips respectively, a ribbon-shaped heater stretched across the heater rests in a manner to pass over the central part of the substrate and having path of its ends fitted to the other end of each of the elastic metal strips so as to be kept tensioned in parallel relationship to the substrate and a layer of thermion emitting material deposited on the central part of the heater.

In the drawings:

FIG, 1 is a perspective view of a cathode member according to an embodiment of the present invention;

FIG. 2 is a plan view of the embodiment of FIG. 1;

FIG. 3 is an elevation of the embodiment of FIG. 1, the right half being a section on axis Y-Y' of FIG. .2;

FIG. 4 is a perspective view of a cathode member according to another embodiment of the invention;

FIG. 5 is a plan view of the embodiment of FIG. 4; and

FIG. 6 is an elevation of the embodiment of FIG. 4, the right half being a section on axis Y-Y of FIG. 5.

FIGS. 1 to 3 jointly represent the cathode member of a cathode ray tube according to an embodiment of the present invention. The cathode member has a press molded substrate 1 prepared from ceramic material. The substrate has its opposite sides 2 (9 mm. long, for example) formed with a groove 3 running all along the length thereof, a part of the outer walls of both ends of each side being curved. On the inside of the bottom part of each end of the opposite sides 2 there is formed an inwardly extending projection 4. As viewed from above, the projections 4 on the opposite sides 2 define an opening having a funnel cross-section.

Perpendicularly across the opposite sides 2 there are formed a pair of heater rests 6 in a manner to cause the top surface of each rest to be flush with those of the opposite sides 2. As clearly seen from FIG. 3, the upper parts of the lateral walls of each rest extend downward in symmetrical relationship relative to the top surface, but the lower part of the outer lateral wall of each rest extends downward perpendicularly to the top surface. Reference numeral 7 denotes a rectangular cavity defined by the heater rests and the opposite sides and having a depth of, for example, 0.5 mm. as measured from the top surface of the heater rest. The cavity 7 has a through hole 8 bored in the centre, said hole having a diameter of, for example, 1.8 mm.

The stepped part 9 at which the vertically extending portion of the outer lateral wall of the heater rest 6 is commenced, defines a narrow void space 10 with that wall of each projection 4 which faces the aforesaid through hole and a part of the inner wall of each of the opposite sides 2.

Because the ceramic substrate 1 having the aforementioned construction is press molded, there is eliminated the drilling step as has been required with the prior art, aifording great convenience in the miniaturisation and mass production of a cathode member.

In the void space 10 there is securely inserted a T-shaped metal strip 11 made of a material whose thermal expansion coefiicient is equal to or slightly smaller than that of the ceramic substrate, such as an alloy of iron-nickel or iron-cobalt-nickel. To describe further, the metal strip has a thickness of, for example, 0.25 mm. Its square portion, 1.7 mm. x 1.5 mm., and narrow rectangular or band-shaped portion, 0.6 mm. X 4.0 mm., are integrally formed into a T-shape. The square broad upper part of the metal strip projects above the top plane of the stepped part 9, and a part of one side of the metal strip 11 is brazed or adhesively bonded to the vertical side wall of the stepped part 9.

Where the metal strip is adhesively bonded to said stepped part 9, the ceramic material of the substrate 1 is preferably porous. In this case, however, the adhesive agent used should be free from a material, such as carbon or lead, which will permeate the porous ceramic material to stain it. The adhesive agent to be used with the cathode member of the present invention may be illustrated by lead-free glass powders, for example, soldering glass containing small amounts of bentoni-te. If, after said adhesive agent is applied, the substrate 1 and metal strip 11 are heated minutes at a temperature of 1100" C. in an inert atmosphere, such as nitrogen or argon, then the metal strip 11 will be suitably bonded to the substrate 1. At 13 of each T-shaped metal strip 11 there is welded an elastic metal strip 12. The upper bent end portion 14 .of this elastic metal strip 12 which is set apart from 13 is adapted to hold a ribbon-shaped heater 15 in place.

The elastic metal strip has its dimensions controlled by .means of a jig so as to retain its flexured state.

,.It will be understood that the portion of the heater lying between the rests 6 is stretched parallel to the flat plane of the substrate 1 which includes the top surface of each rest. The underside of each bent end of the heater 15 and the top side of each bent end 14 of the elastic metal strip 12 are bonded together by spot welding. The spot welding of the heater 15 and elastic metal strip 12 is carried out with the elastic metal strip 12 pressed from the outside to the metal strip 11. Thus, the layer 16 of the electron emitting material can be prevented from unduly deviating from the centre of the through hole 8, even though the elastic metal strip 12 presents some variations in elasticity.

The ribbon-shaped heater 15 preferably consists of a metal alloy having a great tensile strength at elevated temperatures, such as that of nickel-tungsten, or nickelmolybdenum-iron.

The groove 3 formed in the top surface of each of the opposite sides 2 of the substrate 1, together with each heater rest 6, is used as an aid in preventing the increase of surface leak current by causing a part of the material evaporation from the electron emitting layer 16 to be deposited therein.

The aforementioned opening 5 having a funnel crosssection shape allows the spot welding of the ribbon-shaped heater 15 and elastic strips 12, both being very small, to be easily carried out. As seen from FIGS. 2 and 3, the cathode member of the present invention permits all parts to be easily fitted in symmetrical relationship relative to the axes X-X, Y-Y' and Z-Z', so that the dimensional accuracy of the heater can be satisfactorily preserved. Moreover, the heater 15 is fixed to the metal strips 11 attached to the substrate 1 by the aid of the elastic metal strips 12 so that it has an increased quake resistance.

The direct heated cathode member thus constructed is inserted into the first cylindrical grid of the cathode ray tube and caulked to the inner circumferential wall of ,the first grid using a spacer.

There will now be described another embodiment of the invention 'by reference to FIGS. 4 to 6. The same parts of these figures as those of FIGS. 1 to 3 are denoted by the same numerals, and description thereof is omitted.

Numeral 17 designates grooves formed in the opposite sides 2, into which are inserted a pair of cores 18 each slidably and rotatably supporting a cylindrical member 19 that bridges the opposite sides 2. In this embodiment, the top surface of the central part of the substrate 1 is made flush with that of the opposite sides 2 as shown by numeral 20. The central part 20 and grooves 17 should be arranged to prevent the cylindrical member 19 from touching the central part 20.

In this embodiment, the distance between the ribbonshaped heater 15 and substrate 1 can be adjusted by inserting a core 18 of different diameter into the cylindrical member 19. Further, the deformations of the heater 15, due to its expansion or contraction occurring during its operation or cessation of operation are absorbed by the action of rotary cylindrical member 19, so that the heater 15 is saved from being damaged by forced contact with the substrate 1.'Moreover, the absorption of the greater part of the deformations by the cylindrical member 19 prevents the spot welded portion 14 from being loosened.

The direct heated cathode member of this embodiment is caulked to the inner circumferential wall of the first grid of the cathode ray tube in a manner similar to the first-mentioned embodiment.

What is claimed is:

1. A direct heated electron tube cathode member comprising an insulating substrate having a pair of void spaces provided in opposite relationship and a pair of heater rests positioned adjacent to said void spaces in symmetrical relationship, a pair of metal strips fixed in opposite relationship on the substrate perpendicularly to its lengthwise direction in the void spaces so as to face the paired heater rests respectively, a pair of elastic metal strips each having one of its ends attached to the paired metal strips respectively, a ribbon-shaped heater stretched across the heater rests in a manner to pass over the central part of the substrate and having both of its ends fitted to the other end of each of the elastic metal strips so as to be kept tensioned in parallel relationship to the substrate and a layer of thermion emitting material deposited on the central part of the heater.

2. A direct heated electron tube cathode member according to claim 1 wherein the central part of said insulating substrate is formed with a cavity, and said heater rests are constituted by the walls adjacent to the void spaces and by the walls of the cavity.

3. A direct heated electron tube cathode member according to claim 1 wherein the top surface of the central part of said insulating substrate is made flush with its adjacent parts of said insulating substrate and said heater rests are constituted by rotatable members disposed adjacent to the void spaces, the uppermost part of the periphcry of each of said rotatable members being positioned above the top surface of said central part.

4. A direct heated electron tube cathode member according to claim 1, wherein each groove is provided on the top surfaces of the opposite sides of said insulating substrate.

References Cited UNITED STATES PATENTS 2,117,709 5/1938 Davisson 3l334l X 2,732,512 l/1956 Briggs 313-270 X 2,850,663 9/1958 Weindorf 313-278 X (Other references on following page) UNITED STATES PATENTS FOREIGN PATENTS 3,187,216 6/1965 Sciaky 313-27O X 428,945 7/1967 Switzerland. 3,441,767 4/1969 Kerstetter 313341 X 3,444,416 6/1969 Yoshida et a1. 313270 JOHN W. HUCKERT, Primary Examiner 3,465,195 9/1969 Fuchs 313-270 5 A. AM 2,505,668 4/1950 Gomonet 313 211 X I J EsAsslsantExammer 2,650,997 9/1953 Watrous 313-38 U 5 L 2,805,354 9/ 1957 Lemmers et a1 313193 313 2 9, 270 

